The present invention relates to a stencil sheet transfer method of an apparatus for carrying out stencil printing by thermosensitively perforating a desired image to a stencil sheet and transcribing ink from perforated portions of a stencil area of the thermosensitively perforated stencil sheet onto a print sheet. Particularly, the present invention relates to a stencil sheet transfer method of the apparatus suitable for a case of carrying out stencil printing of a desired image by multiple colors.
There has already been known a stencil printing apparatus for carrying out desired printing by mounting stencil sheet thermosensitively perforated with a desired image onto a drum in a cylindrical shape and making ink supplied from inside of the drum transcribe onto a print sheet by permeating the ink from perforated portions of the stencil sheet.
According to a stencil printing machine of this kind, the stencil sheet wound in a shape of a roll is transferred between a thermal head and a platen roller constituting a perforating section. The stencil sheet is transferred by a platen motor for driving the platen roller. Further, the stencil sheet is perforated by thermosensitive perforation by the thermal head. The perforated stencil sheet is transferred toward a drum by a stencil sheet feeding section constituted by transfer rollers and the like. Further, the stencil sheet is wound around a peripheral wall of the drum and is set. When the perforated stencil sheet is set to the peripheral wall of the drum, ink is supplied from inside of the drum to a surface of the peripheral wall in accordance with rotation of the drum. Further, the ink is pushed out from the perforated portions of the perforated stencil sheet.
When a print sheet supplied from a sheet supply base is made to pass between the peripheral wall of the drum and a press roller applied with predetermined pressure in synchronism with the above-described operation, the ink is transcribed onto the print sheet by passing through the perforated portions of the perforated stencil sheet. Thereby, the print sheet is printed with desired image and the printed print sheet is discharged to a print sheet discharge base.
In the meantime, according to the above-described stencil printing machine, in transferring the stencil sheet to the drum, there is adopted a technology of differentiating stencil drive speed of a perforating section from transfer speed of a stencil sheet transferring section in order to prevent meandering.
Generally, according to the stencil printing machine, the transfer speed of the stencil sheet transferring section is set to be faster than the stencil drive speed of the perforating section. Therefore, perforating operation is carried out at the perforating section while exerting pertinent tension to the stencil sheet by the stencil sheet transferring section. Further, actual stencil speed of the stencil sheet at the perforating section at this occasion, is made to be substantially the same as the stencil drive speed set by a platen motor drive circuit.
However, when a distance of transferring the stencil sheet from the perforating section to the drum is long, the tension of the stencil sheet is increased. Further, the actual stencil speed of the stencil sheet becomes proximate to the transfer speed of the stencil sheet transferring section. Thereby, the stencil sheet is dragged in perforating operation and image elongation is produced.
Further, when there are provided a plurality of drums and the transfer distance of the stencil sheet differs respectively thereby, the stencil speed differs in accordance with the transfer distance, which causes elongation and contraction of image. Further, in carrying out printing of multiple color and multiple edition by using a plurality of drums, when there causes elongation and contraction of image to degrees which differ by respective editions, it becomes impossible to overlap and print all of the editions without shift.
The present invention has been carried out in view of the above-described problem and it is an object thereof to optimize stencil drive speed in perforating operation by detecting a point of passing stencil sheet by a sensor. Further, it is another object thereof to carry out stencil printing having excellent reproducibility by reducing elongation and contraction of image of the stencil sheet thereby.